This blog post is odd because it keeps on hinting about a difference between `-r' and `-R' and links to the source code but never actually says what it is. I'll quote the OpenBSD manual that the post mentions but does not link to for some reason:

> Historic versions of the cp utility had an -r option. This implementation supports that option; however, its use is strongly discouraged, as it does not correctly copy special files, symbolic links or FIFOs.

https://man.openbsd.org/cp

> links to the source code but never actually says what it is.

The snippet of code makes it very clear what the difference is, no?

flag_copy_as_regular = 1 VS flag_copy_as_regular = 0, where regular would be a "regular" and not "special" file.